Intermetallic films of two or more elements arc used as resistors or diffusion barriers in semiconductor devices. The intermetallic films are normally deposited onto the semiconductor wafers via the physical vapor deposition (PVD) process. In the PVD process, a sputter target material is bombarded by a plasma or ion beam, which dislodges particles of sputter target material from the sputter surface. These dislodged particles are then deposited onto the semiconductor wafer as a thin film.
Intermetallic sputter targets of two or more elements can be produced either by powder metallurgy or casting techniques. The powder metallurgy method provides a more uniform microstructure than the casting method with respect to grain size distribution, which is an important parameter for controlling thin film properties. Furthermore, due to large differences in the melting points of individual elements comprising many intermetallic target materials, the casting method is less favorable.
The powder metallurgy technique may provide either multiple-phase metallic target structures or single-phase intermetallic target structures, depending on the forming process and the properties of the individual elements. A disadvantage of multiple-phase metallic structures is that due to the difference in sputtering rate between individual elements, the uniformity of the film composition may be inferior to that obtained from single-phase intermetallic compounds. For example, in a multiple-phase Ti--Al sputter target, aluminum will sputter faster than titanium. For a single-phase TiAl.sub.3 compound, the intermetallic compound sputters at a consistent rate, and therefore may contribute to a more uniform composition for the deposited film.
The prior powder metallurgy technique used to obtain intermetallic sputter targets involved synthesizing the metallic powders in a heating furnace without pressure, whereby the individual metals react to form chunks of intermetallic material. A milling or crushing process is then required to fine the sintered chunks to a powder consistency. The powder may then be pressed to form a high-density intermetallic sputter target. This prior method employs two separate steps with intermediate milling to achieve the pressed sputter target. The milling process tends to contribute to contamination of the sputter target material, which may cause non-uniformity of the deposited thin film.
There is thus a need to develop a method for producing high-density intermetallic sputter targets that minimizes contamination from the processing method.